Substrates containing narrow or high spatial resolution structures upon their surfaces are useful to a number of different industrial applications. A variety of known methods are currently used for forming ultra-fine structures and patterns on substrates and in particular nanowires or microwires having widths or diameters of the order of 10−9 to 10−6 metres.
Various top-down techniques for forming ultra-narrow wires are known, in particular lithography and electrophoresis. Additionally, bottom-up approaches to nano- or microwire production are currently used which assemble effectively one dimensional, or otherwise ultra-narrow structures by combining constituent particles. One example of an existing synthesis technique for nano-structures uses electrohydrodynamic activity triggered by the application of DC voltage to a fluid ink. Such electrohydrodynamics-based approaches allow fine structures to be printed upon substrates, however these techniques require a minimum degree of electrical conductivity in the substrate, so that a DC bias can be applied in all locations of the substrate. Therefore, electrohydrodynamics-based methods are limited to particular types of substrates having a specific range of dielectric and conductive properties. Indeed, for most electrohydrodynamic jet printing methods it is required or preferable that the substrate is sufficiently conductive to dissipate the charge that may otherwise accumulate locally. Although some different techniques for addressing this issue and using substrates having limited conductivity with such methods have been proposed, these necessitate a more complicated printing process.
Alternative known techniques employ photolithographic methods, wherein micropatterns are applied by transferring a predetermined geometry of a desired structure of pattern from a photomask to a light-sensitive substance upon the substrate, whereupon the exposure pattern is deposited or engraved in a predetermined pattern upon the substrate material behind the light-sensitive photoresist. While photolithography facilitates the rapid production of complex micropatterns which may have high spatial resolutions and complex geometries, the lines which may be produced by such methods are necessarily flat in profile, and so are of limited use in applications that require a structure to be formed that has a height of a given value or comparable to its width.
There exists a need for a method of producing ultra-narrow lines, having widths even less than 1 micrometre, made up of a variety of different inorganic constituent materials. In particular, there is a demand in a number of different applications for an efficient and scalable technique for forming fine conductive lines or patterns, as well as structures having semiconductor properties.
Examples of typical applications in which such a method of producing high-resolution micropatterns comprising a range of materials and disposed upon a range of different substrates may be useful include production of semiconducting quantum dots, for light emission applications, light absorbing semiconducting nanoparticles for photovoltaic energy conversion, or other dielectric materials for sensing applications.